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<p class="HeadingPart">
    Extensible 3D (X3D)<br />
    Part 1: Architecture and base components</p>

<p class="HeadingClause">7 Core component</p>
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<img class="x3dbar" src="../../Images/x3dbar.png" ALT="--- X3D separator bar ---" width="430" height="23">

<h1><img class="cube" src="../../Images/cube.gif" alt="cube">
<a name="Introduction"></a>7.1 Introduction</h1>

<h2><a name="Name"></a>7.1.1 Name</h2>

<p>The name of this component is &quot;Core&quot;. This name shall be used when referring 
to this component in the COMPONENT statement (see <a href="#COMPONENTStatement">
7.2.5.4 Component statement</a>).</p>

<h2><a name="Overview"></a>7.1.2 Overview</h2>

<p>This clause describes the Core component of this part of ISO/IEC 19775. The 
  Core component supplies the base functionality for the X3D run-time system, including 
  the abstract base node type, field types, the event model, and routing. 
<a href="#t-Topics">Table 7.1</a> lists the major topics in this clause.</p>

<div class="CenterDiv">

<p class="TableCaption">
<a name="t-Topics"></a>
Table 7.1 &#8212; Topics</p>

  <table class="topics">
    <tr> 
      <td>
        <ul>
          <li><a href="#Introduction">7.1 Introduction</a>
            <ul>
              <li><a href="#Name">7.1.1 Name </a></li>
              <li><a href="#Overview">7.1.2 Overview</a></li>
            </ul></li>
          <li><a href="#Concepts">7.2 Concepts</a>
            <ul>
              <li><a href="#Overviewofthecore">7.2.1 Overview of the core</a></li>
              <li><a href="#BindableChildrenNodes">7.2.2 Bindable children nodes</a></li>
              <li><a href="#Sensors">7.2.3 Sensors</a></li>
              <li><a href="#Metadata">7.2.4 Metadata</a>
                <ul>
                  <li><a href="#MetadataOverview">7.2.4.1 Overview</a></li>
                  <li><a href="#DataTypesForMetadata">7.2.4.2 Data types for metadata</a></li>
                  <li><a href="#AssigningMetadataToEntireX3DWorld">7.2.4.3 Integration with X3D worlds</a></li>
                  <li><a href="#AssigningMetadataToEntireX3DWorld">7.2.4.4 Assigning metadata to an entire X3D world</a></li>
                </ul></li>
              <li><a href="#AbstractX3DStructure">7.2.5 Abstract X3D structure</a>
                <ul>
                  <li><a href="#Organization">7.2.5.1 Organization</a></li>
                  <li><a href="#HeaderStatement">7.2.5.2 Header statement</a></li>
                  <li><a href="#PROFILEStatement">7.2.5.3 PROFILE statement</a></li>
                  <li><a href="#COMPONENTStatement">7.2.5.4 COMPONENT statement</a></li>
                  <li><a href="#METAStatement">7.2.5.5 META statement</a></li>
					<li><a href="#ROUTEStatement">7.2.5.6 ROUTE statement</a></li>
					<li><a href="#PROTOStatement">7.2.5.7 PROTO statement</a></li>
					<li><a href="#EXTERNPROTOStatement">7.2.5.8 EXTERNPROTO 
					statement</a></li>
                </ul></li>
            </ul></li>
          <li><a href="#Abstracttypes">7.3 Abstract types</a>
            <ul>
              <li><a href="#X3DBindableNode">7.3.1 <i>X3DBindableNode</i></a></li>
              <li><a href="#X3DChildNode">7.3.2 <i>X3DChildNode</i></a></li>
				<li><a href="#X3DInfoNode">7.3.3 <i>X3DInfoNode</i></a></li>
              <li><a href="#X3DMetadataObject">7.3.4 <i>X3DMetadataObject</i></a></li>
              <li><a href="#X3DNode">7.3.5 <i>X3DNode</i></a></li>
              <li><a href="#X3DPrototypeInstance">7.3.6 <i>X3DPrototypeInstance</i></a></li>
              <li><a href="#X3DSensorNode">7.3.7 <i>X3DSensorNode</i></a></li>
            </ul></li>
          <li><a href="#Nodereference">7.4 Node reference</a>
            <ul>
              <li><a href="#MetadataDouble">7.4.1 MetadataDouble</a></li>
              <li><a href="#MetadataFloat">7.4.2 MetadataFloat</a></li>
              <li><a href="#MetadataInteger">7.4.3 MetadataInteger</a></li>
              <li><a href="#MetadataSet">7.4.4 MetadataSet</a></li>
              <li><a href="#MetadataString">7.4.5 MetadataString</a></li>
				<li><a href="#WorldInfo">7.4.6 WorldInfo</a></li>
            </ul></li>
          <li><a href="#SupportLevels">7.5 Support levels</a>
        </ul>
        <ul>
          <li><a href="#t-Topics">Table 7.1 &#8212; Topics</a></li>
          <li><a href="#t-Coresupportlevels">Table 7.2 &#8212; Core component support levels</a></li>
        </ul>
      </td>
    </tr>
  </table>
</div>

<h1><img class="cube" src="../../Images/cube.gif" alt="cube">
<a name="Concepts"></a>
7.2 Concepts </h1>

<h2><a name="Overviewofthecore"></a>
7.2.1 Overview of the core</h2>

<p>The Core component provides the minimum functionality required by all X3D-compliant 
  implementations. The Core component supplies the following abstract 
constructs:</p>

<ol type="a">
  <li>X3D field types descended from the abstract type <i>
	<a href="../fieldsDef.html#X3DField">X3DField</a></i>;</li>
  <li>the base abstract node types <i><a href="#X3DNode">X3DNode</a></i> and <i>
	<a href="#X3DPrototypeInstance">X3DPrototypeInstance</a></i>;</li>
  <li>commonly used interfaces such as <i><a href="#X3DBindableNode">X3DBindableNode</a></i> and <i>
  <a href="networking.html#X3DUrlObject">X3DUrlObject</a></i>;</li>
  <li>the X3D event model and routing; </li>
  <li>abstract file structure; and </li>
  <li>prototyping.</li>
</ol>

<p>The Core component is a prerequisite component for all other X3D components.</p>

<p>The Core component may be supported at a variety of <a href="#SupportLevels">levels</a>, 
  allowing for a range of implementations that are conformant to the X3D architecture, 
  object model and event model. For more information on these topics, 
see <a href="../concepts.html">4. Concepts</a>.</p>

<h2><a name="BindableChildrenNodes"></a>7.2.2 Bindable children nodes</h2>

<p>Several X3D nodes, such as <a href="enveffects.html#Background">Background</a>, 
<a href="enveffects.html#TextureBackground">TextureBackground</a>, 
<a href="enveffects.html#Fog">Fog</a>, 
<a href="navigation.html#NavigationInfo">NavigationInfo</a>, and 
<a href="navigation.html#Viewpoint">Viewpoint</a> are bindable children 
  nodes, inheriting from the abstract node type 
<a href="#X3DBindableNode">X3DBindableNode</a>. 
  These nodes have the unique behaviour that only one of each type can be bound 
per layer 
  (<i>i.e.</i>, affect the user's experience) at any instant in time. The browser 
  shall maintain an independent, separate stack for each type of bindable node 
in each layer. 
  If there is no <a href="layering.html#LayerSet">LayerSet</a> node defined, there shall be only one set of binding 
stacks that apply to all nodes in the scene graph. Each of these nodes includes a <i>set_bind</i> inputOnly field and an <i>isBound</i> 
outputOnly field. The <i>set_bind</i> inputOnly field is used to move a given node to and from 
  its respective top of stack. A <span class="code">TRUE</span> value sent to the <i>set_bind </i>
inputOnly field 
  moves the node to the top of the stack; sending a <span class="code">FALSE</span> value removes it from 
  the stack. The <i>isBound</i> event is output when a given node is:</p>

<ol type=a>
  <li>moved to the top of the stack;</li> 
  <li>removed from the top of the stack;</li>
  <li>pushed down from the top of the stack by another node being placed on top.</li> 
</ol>

<p>That is, <i>isBound</i> events are sent when a given node becomes, or ceases 
  to be, the active node. The node at the top of the stack (the most recently bound 
  node) is the active node for its type and is used by the browser to set the 
  world state. If the stack is empty (<i>i.e.</i>,&nbsp;either the X3D file has no bindable 
  nodes for a given type or the stack has been popped until empty), the default 
  field values for that node type are used to set world state. The results are 
  undefined if a multiply instanced (DEF/USE) bindable node is bound.</p>
<p>Bindable nodes only affect the binding stacks of the layer in which they are 
defined.</p>

<p>The following rules describe the behaviour of the binding stack for a node 
  of type <i>&lt;bindable node&gt;, </i>
(Background, TextureBackground, Fog, NavigationInfo, or Viewpoint):</p>

<ol type=a start=4>
  <li>During read, the first encountered <i>&lt;bindable node&gt;</i> in each 
	layer is bound 
    by pushing it to the top of the <i>&lt;bindable node&gt;</i> stack for that 
	layer. Nodes 
    contained within files referenced by <a href="networking.html#Inline">Inline</a> 
  nodes, within the strings passed to 
    the Browser.createX3DFromString() method, or within X3D files passed to 
    the Browser.createX3DFromURL() method (see
  <a href="../references.html#[I19775_2]">Part 2 of ISO/IEC 19775</a>) 
are not candidates for the first encountered <i>&lt;bindable 
    node&gt;</i>. The first node within a locally defined prototype instance is a valid candidate 
    for the first encountered <i>&lt;bindable node&gt;</i>. The first encountered 
    <i>&lt;bindable node&gt;</i> sends an <i>isBound </i><span class="code">TRUE</span><i> </i>event.</li> 
  <li>When a <i>set_bind</i> <span class="code">TRUE</span> event is received by a <i>&lt;bindable node&gt;</i>,<ol type=1>
      <li>If it is <u>not</u> on the top of the stack: the current top of stack 
        node sends an <i>isBound</i> <span class="code">FALSE</span> event. The new node is <u>moved</u> 
        to the top of the stack and becomes the currently bound <i>&lt;bindable 
        node&gt;</i>. The new <i>&lt;bindable node&gt;</i> (top of stack) sends 
        an <i>isBound </i><span class="code">TRUE</span><i> </i>event.</li> 
      <li>If the node is already at the top of the stack, this event has no effect.</li>
    </ol>
  <li>When a <i>set_bind</i> <span class="code">FALSE</span> event is received by a <i>&lt;bindable node&gt;</i> 
    in the stack, it is removed from the stack. If it was on the top of the stack,<ol type=1>
      <li>it sends an <i>isBound</i> <span class="code">FALSE</span> event;</li> 
      <li>the next node in the stack becomes the currently bound <i>&lt;bindable 
        node&gt; </i>(<i>i.e.</i>,&nbsp;pop)<i> </i>and issues an<i> isBound </i>
		<span class="code">TRUE</span><i> 
        </i>event. </li>
    </ol>
  <li>If a <i>set_bind</i> <span class="code">FALSE</span> event is received by a node not in the stack, 
    the event is ignored and <i>isBound</i> events are not sent.</li> 
  <li>When a node replaces another node at the top of the stack, the <i>isBound</i>
  <span class="code">TRUE</span> and <span class="code">FALSE</span> output 
  events from the two nodes are sent simultaneously (<i>i.e.</i>, with 
    identical timestamps).</li> 
  <li>If a bound node is deleted, it behaves as if it received a <i>set_bind </i>
  <span class="code">FALSE</span> 
    event (see f above). </li>
</ol>

        <p>The results are undefined if a bindable node is bound 
          and is the child of an <a href="navigation.html#LOD">LOD</a>, 
		<a href="group.html#Switch">Switch</a>, or any node or prototype that disables 
          its children. If a bindable node is bound that results in collision 
          with geometry, the browser shall perform its self-defined navigation 
          adjustments as if the user navigated to this 
point (see <a href="navigation.html#Collision">23.3.2 Collision</a>).</p>

<h2><a name="Sensors"></a>7.2.3 Sensors</h2>

<p>Sensors are nodes that generate events based on external inputs to the scene 
graph, such as user input, changes to the viewing environment, messages from the 
network or ticks of the system clock. X3D defines the following types of<br>
sensors:</p>
<ol type="a">
  <li>Pointing device sensors (see <a href="pointingsensor.html">20 Point 
  device sensor component</a>),</li>
  <li>Environmental sensors (see <a href="envsensor.html">22 Environmental 
  sensor component</a>),</li>
  <li>Key device sensors (see <a href="keyboard.html">21 Key device sensor 
  component</a>),</li>
  <li>Load sensors (see <a href="networking.html">9 Networking component</a>),</li>
  <li>Time sensors (see <a href="time.html">8 Time component</a>), and</li>
	<li>Picking sensors (see <a href="picking.html">38 Picking sensor component</a>).</li>
</ol>

<p>Sensors are children nodes in the hierarchy and therefore may be parented by 
grouping nodes as described in <a href="group.html#Groupingandchildrennodes">
10.2.1 Grouping and children node types</a>.</p>

<p>Each type of sensor defines when an event is generated. The state of the 
scene graph after several sensors have generated events shall be as if each 
event is processed separately, in order. If sensors generate events at the same 
time, the state of the scene graph will be undefined if the results depend on 
the ordering of the events.</p>

<p>It is possible to create dependencies between various types of sensors.</p>
<p class="Example">EXAMPLE&nbsp; A TouchSensor may result in a change to a VisibilitySensor node&#39;s 
transformation, which in turn may cause the VisibilitySensor node&#39;s visibility 
status to change.</p>
<p>For a detailed description of how dependencies among sensors 
are handled during execution, see <a href="../concepts.html#Executionmodel">
4.4.8.3 Execution model</a>.</p>

<h2><a name="Metadata"></a>7.2.4 Metadata</h2>
<h3><a name="MetadataOverview"></a>7.2.4<i>.</i>1 Overview</h3>
<p>Metadata is information that is associated with the objects of the X3D world 
but is not a direct part of the world representation. This part of ISO/IEC 19775 
defines an abstract interface <i><a href="#X3DMetadataObject">X3DMetadataObject</a></i> that identifies a node as 
containing metadata and metadata nodes that specify metadata values in various 
data types.</p>
<h3><a name="DataTypesForMetadata"></a>7.2.4.2 Data types for metadata</h3>
<p>This part of ISO/IEC 19775 specifies three basic representation types:&nbsp; 
strings, single-precision and double-precision floating point values, and 
integers. Each piece of metadata has two additional strings that describe:</p>
<ol type="a">
  <li>the metadata standard (if any) from which the metadata specification 
  emanates, and </li>
  <li>the identification for the particular piece of metadata being provided.
  </li>
</ol>
<p>The <a href="#MetadataSet">MetadataSet</a> node is provided to support cases when a specific set of 
metadata requires more than a single data type.</p>
<p class="Example">NOTE&nbsp; Since a metadata node is derived from <i>
<a href="#X3DNode">X3DNode</a></i>, 
the metadata node may itself have metadata.</p>
<h3><a name="IntegrationWithX3DWorlds"></a>7.2.4.3 Integration with X3D worlds</h3>
<p>The <i><a href="#X3DNode">X3DNode</a></i> abstract node type specifies an SFNode field <i>metadata</i> 
that may only be populated with nodes derived from <i>
<a href="#X3DMetadataObject">X3DMetadataObject</a></i>. If 
the <i>metadata</i> field is empty, no metadata is associated with the node. 
Since all nodes in X3D are derived from <i>X3DNode</i>, metadata may be placed anywhere 
in an X3D world.</p>
<p>Metadata is not included as part of the depiction of an X3D world. However, 
metadata nodes may have a DEF name and the values of the fields of a metadata 
node may be accessed by SAI services and can be accessed using routing.</p>
<p>The content of the value field of a metadata node is not interpreted by the 
X3D browser.</p>
<p>Metadata may also be attached to other X3D nodes by setting the metadata 
field of that node to a node derived from the X3DMetadataNode abstract node 
type.</p>
<h3><a name="AssigningMetadataToEntireX3DWorld"></a>7.2.4.4 Assigning metadata 
to an entire X3D world</h3>
<p>The META statement (see <a href="#METAStatement">7.2.5.5 META statement</a>) 
may be used to assign metadata to the entire world. The content of the META 
statement is accessible using the SAI. If it is desired that metadata 
information that applies to the entire world be provided for access through 
routing, a <a href="group.html#WorldInfo">WorldInfo</a> node containing the 
metadata in its metadata field may be inserted as a root node.</p>

<h2><a name="AbstractX3DStructure"></a>7.2.5 Abstract X3D structure</h2>
<h3><a name="Organization"></a>7.2.5.1 Organization</h3>
<p>An X3D world is conceptually defined as a sequence of statements organized 
conceptually as a file. The first item in the file is the Header statement. The 
second item in the file is the PROFILE statement. The PROFILE statement may be 
optionally followed by one or more COMPONENT statements. The remainder of the 
file consists of the other elements defined in this part of ISO/IEC 19775. 
Optional META statements shall follow any COMPONENT statements or, if there are 
no COMPONENT statements, the PROFILE statement. All other statements shall 
follow the statements described above.</p>
<p>ROUTE statements are used to specify the pathways for allowed transmission of 
events. These statements link a field in one node to a field of the same field 
type in another node.</p>
<p>PROTO statements are used to specify new node types. Such statements assign a 
name to the new node type along with a declaration of the interface for the new 
node type. This is followed by a definition for the node type functionality.</p>
<p>EXTERNPROTO statements are used to specify an interface to PROTO or 
EXTERNPROTO statements located externally to the local file. </p>
<p>Any additional X3D content loaded into the scene via 
<a href="networking.html#Inline">Inline</a> nodes or scenes 
loaded using createX3DFromStream, createX3DFromString, or createX3DFromUrl, 
shall be declared as having a profile that has an equal or smaller set of 
required functionality; <i>i.e.</i>, there can be no components explicitly declared, or 
implied by the profile in that content, that requires functionality not declared 
in the original profile and component declarations for the containing scene.</p>
<p>Although an X3D world is described as being contained in a file, the file may 
be conceptual and created dynamically during run-time as described in
<a href="../references.html#[I19775_2]">Part 2 of ISO/IEC 19775</a>.</p>
<h3><a name="HeaderStatement"></a>7.2.5.2 Header statement</h3>
<p>The Header statement is an encoding-dependent statement containing the 
following elements:</p>
<ol type="a">
  <li>identification of the standard being supported (for this standard, this is 
  &quot;X3D&quot;);</li>
	<li>version of the standard being supported (for this version of this part 
	of ISO/IEC 19775, the version number is &quot;3.2&quot;);</li>
  <li>identification of the character encoding being supported (for this 
  standard, this shall be &quot;UTF-8&quot;), and</li>
  <li>optional comments that may apply to the file.</li>
</ol>
<p>While the exact representation of this information is dependent on the 
encoding, this information shall always be stored as human-readable text.</p>
<h3><a name="PROFILEStatement"></a>7.2.5.3 PROFILE statement</h3>
<p>Every X3D application shall declare a profile at the beginning of execution. 
This declaration tells the browser the exact set of components and their support 
levels that are required for the application to run, allowing for a browser to 
dynamically load the appropriate components if it so desires, and providing a 
mechanism for strict conformance should the browser choose to enforce it. If a 
browser supports the combination of declared profile and components (see
<a href="#COMPONENTStatement">7.2.5.4 COMPONENT statement</a>), it may proceed 
with presenting the world; otherwise, it shall fail.</p>
<p>The profile is declared via a PROFILE statement immediately following the 
Header statement at the top of the file. The form of the PROFILE statement is:</p>
<blockquote>
  <p><span class="code">PROFILE &lt;name&gt;</span></p>
</blockquote>
<p>where name is a string that does not contain whitespace.</p>
<p>The following profiles are defined in this standard:</p>
<ol type="a">
  <li>Core (see <a href="../coreprofile.html">A Core profile</a>),</li>
  <li>Interchange (see <a href="../interchange.html">B Interchange profile</a>),</li>
  <li>Interactive (see <a href="../interactive.html">C Interactive profile</a>),</li>
  <li>MPEG-4 interactive (see <a href="../MPEG4interactive.html">D MPEG-4 
  interactive profile</a>),</li>
  <li type="a" value="5">Immersive (see <a href="../immersive.html">E Immersive 
	profile</a>),</li>
	<li type="a">Full (see <a href="../fullProfile.html">F Full profile</a>), 
	and </li>
	<li type="a">CADInterchange (see <a href="../CADInterchange.html">H CAD 
	interchange profile</a>).</li>
</ol>
<p>The profile name is implicitly qualified by the version number of the 
standard (see <a href="#HeaderStatement">7.2.5.2 Header statement</a>). Browsers 
shall use both the profile name and the version number to determine the specific 
characteristics of the profile.</p>
<h3><a name="COMPONENTStatement"></a>7.2.5.4 COMPONENT statement</h3>
<p>X3D applications may explicitly declare additional components required for 
the application to run. This is useful for combining features that do not appear 
together in a predefined profile, such as adding humanoid animation support to 
the Immersive profile. If a browser supports the combination of declared profile 
and components, it may proceed with presenting the world; otherwise, it shall 
fail.</p>
<p>Declaring a component in a file shall only add support for nodes and 
functionality defined in that component at the requested support level. Nodes 
that are defined as part of the prerequisite components (see
<a href="../concepts.html#Basecomponents">4.5.3 Base Components</a>) shall not 
be automatically included. A user shall declare all components and levels for 
the nodes and/or functionality being used either explicitly through the use of 
the COMPONENT statement or implicitly through the PROFILE statement.</p>
<p>Components are declared by COMPONENT statements at the top of the file, 
immediately following the PROFILE statement but preceding any other content. The 
form of the component statement is:</p>
<blockquote>
  <p><span class="code">COMPONENT &lt;name&gt; &lt;level&gt;</span></p>
</blockquote>
<p>where &lt;name&gt; is a string that does not contain whitespace, and &lt;level&gt; is a 
positive integer.</p>
<p>If support for a component at the desired level is implied by the 
application&#39;s declared profile, the declaration for that component is 
unnecessary but may be included.</p>

<h3><a name="METAStatement"></a>7.2.5.5 META statement</h3>
<p>X3D applications may explicitly declare metadata about the world being 
defined. This is done by adding one or more META statements that contain such 
information. Such statements do not affect the scene graph but simply provide 
additional information in the world.</p>
<p>Metadata is specified by META statements at the top of the file, 
immediately following the PROFILE and COMPONENT statements but preceding any other content. The 
form of the META statement is:</p>
<blockquote>
  <p><span class="code">META &lt;key&gt; &lt;data&gt;</span></p>
</blockquote>
<p>where &lt;key&gt; is a string that identifies the metadata and &lt;data&gt; is a 
string that defines the value for the  metadata identified by &lt;key&gt;.</p>

<h3><a name="ROUTEStatement"></a>7.2.5.6 ROUTE statement</h3>
<p>X3D applications specify connections between fields of one node to fields of 
other nodes using the ROUTE statement. See <a href="../concepts.html#Routes">4.4.8.2 Routes</a> 
for a general discussion of routes.</p>
<p>ROUTE statements may appear anywhere in the file and have the following form:</p>
<blockquote>
  <p><span class="code">ROUTE &lt;fromNodeName&gt; &lt;fromFieldName&gt; &lt;toNodeName&gt; &lt;toFieldName&gt;</span></p>
</blockquote>
<p>where &lt;fromNodeName&gt; identifies the node that will generate an event, &lt;fromFieldName&gt; 
is the name of the field in the generating node from which the event will 
eminate, &lt;toNodeName&gt; identifies the node that will receive an event, and &lt;toFieldName&gt; 
identifies the field in the destination node that will receive the event.</p>

<h3><a name="PROTOStatement"></a>7.2.5.7 PROTO statement</h3>
<p>New node types may be defined by X3D applications through use of the PROTO 
statement as specified in <a href="../concepts.html#PROTOdefinitionsemantics">
4.4.4 Prototype semantics</a>.</p>
<p>PROTO statements may appear anywhere in the file and have the following form:</p>
<blockquote>
  <p><span class="code">PROTO &lt;protoName&gt; &lt;protoInterfaceDeclaration&gt; &lt;protoDefinition&gt;</span></p>
</blockquote>
<p>The &lt;protoName&gt; specifies the name for the new node type.</p>
<p>The &lt;protoInterfaceDeclaration&gt; specifies a list of field definitions. Each 
field definition specifies the data type, access type, and name for the field. 
For initializeOnly and inputOutput fields, the default value is also specified. 
See <a href="../concepts.html#PROTOinterfacedeclsemantics">4.4.4.2 PROTO interface declaration semantics</a> 
for details.</p>
<p>The &lt;protoDefinition&gt; consists of a list of nodes the first of which is used 
to specify the node type for the prototype. This list may instantiate other 
prototypes provided that the definitions of the referenced prototypes precede 
this PROTO statement. See <a href="../concepts.html#PROTOdefinitionsemantics">4.4.4.3 PROTO definition semantics</a> 
for details.</p>

<h3><a name="EXTERNPROTOStatement"></a>7.2.5.8 EXTERNPROTO statement</h3>
<p>Externally defined new node types may be used by X3D applications by 
referencing their definition using the EXTERNPROTO statement as specified in
<a href="../concepts.html#EXTERNPROTOsemantics">4.4.5 External prototype 
semantics</a>.</p>
<p>EXTERNPROTO statements may appear anywhere in the file and have the following 
form:</p>
<blockquote>
  <p><span class="code">EXTERNPROTO &lt;externprotoName&gt; &lt;externprotoInterfaceDeclaration&gt; 
	&lt;externprotoURL&gt;</span></p>
</blockquote>
<p>The &lt;externprotoName&gt; specifies the name for the new node type.</p>
<p>The &lt;externprotoInterfaceDeclaration&gt; specifies a list of field definitions. 
Each field definition specifies the data type, access type, and name for the 
field. The default value for intializeOnly and inputOutput field is derived as 
specified in <a href="../concepts.html#EXTERNPROTOInterfaceSemantics">4.4.5.2 
EXTERNPROTO interface semantics</a>.</p>
<p>The &lt;externprotoURL&gt; specifies the location of the definition for the 
externally defined prototype. See
<a href="../concepts.html#EXTERNPROTOURLSemantics">4.4.5.3 EXTERNPROTO URL 
semantics</a> for details.</p>

<h1><a name="Abstracttypes"></a>
7.3 Abstract types</h1>

<h2><a name="X3DBindableNode"></a>7.3.1 <i>X3DBindableNode</i></h2>

<pre class="node">X3DBindableNode : X3DChildNode {
  SFBool [in]     set_bind
  SFNode [in,out] metadata NULL [X3DMetadataObject]
  SFTime [out]    bindTime
  SFBool [out]    isBound
}
</pre>

  <p> X3DBindableNode is the abstract base type for all bindable 
    children nodes, including <a href="enveffects.html#Background">Background</a>,
	<a href="enveffects.html#TextureBackground">TextureBackground</a>, 
	<a href="enveffects.html#Fog">Fog</a>,
	<a href="navigation.html#NavigationInfo">NavigationInfo</a> 
    and <a href="navigation.html#Viewpoint">Viewpoint</a>. For complete discussion of bindable behaviors, see <a href="#BindableChildrenNodes">
  7.2.2 Bindable children nodes</a>.</p>


<h2><a name="X3DChildNode"></a>
7.3.2 <i>X3DChildNode</i></h2>

<pre  class="node">X3DChildNode : X3DNode { 
  SFNode [in,out] metadata NULL [X3DMetadataObject]
}
</pre>

<p>This abstract node type indicates that the concrete nodes that are instantiated 
  based on it may be used in <i>children, addChildren, and removeChildren</i> 
  fields.</p>

<p>More details on the <i>children</i>, <i>addChildren</i>, and <i>removeChildren</i> 
  fields can be found in <a href="group.html#Groupingandchildrennodes">10.2.1 Grouping 
  and children node types</a>.</p>


<h2><a name="X3DInfoNode"></a>7.3.3 <i>X3DInfoNode</i></h2>

<pre class="node">X3DInfoNode : X3DChildNode { 
  SFNode [in,out] metadata NULL [X3DMetadataObject]
}
</pre>

<p>This is the base node type for all  nodes that contain only information 
without visual semantics.</p>


<h2><a name="X3DMetadataObject"></a>7.3.4 <i>X3DMetadataObject</i></h2>

<pre class="node">X3DMetadataObject { 
  SFString [in,out] name      &quot;&quot;
  SFString [in,out] reference &quot;&quot; 
}</pre>
<p>This abstract interface is the basis for all metadata nodes. The interface is 
inherited by all metadata nodes.</p>
<p>The specification of the <i>reference</i> field is optional. If provided, it 
identifies the metadata standard or other specification that defines the <i>name</i> 
field. If the <i>reference</i> field is not provided or is empty, the meaning of 
the <i>name</i> field is considered implicit to the characters in the string.</p>


<h2><a name="X3DNode"></a>7.3.5 <i>X3DNode</i></h2>

<pre class="node">X3DNode {
  SFNode [in,out] metadata NULL [X3DMetadataObject]
}
</pre>

<p>This abstract node type is the base type for all nodes in the X3D system.</p>


<h2><a name="X3DPrototypeInstance"></a>7.3.6 <i>X3DPrototypeInstance</i></h2>

<pre class="node">X3DPrototypeInstance : X3DNode {
  SFNode [in,out] metdata NULL [X3DMetadataObject]
}
</pre>

<p>This abstract node type is the base type for all prototype instances in the 
  X3D system. Any user-defined nodes declared with PROTO or EXTERNPROTO are instantiated 
  using this base type. An <i>X3DPrototypeInstance</i> may be place anywhere in the scene 
  graph where it is legal to place the first node declared within the prototype 
  instance. For example, if the base type of first node is <i>X3DAppearanceNode</i>, 
  that prototype may be instantiated anywhere in the scene graph that allows for 
  an appearance node (<span class="example">EXAMPLE&nbsp; Shape</span>).</p>


<h2><a name="X3DSensorNode"></a>
7.3.7 <i>X3DSensorNode</i></h2>


<pre class="node">X3DSensorNode  : X3DChildNode {
  SFBool [in,out] enabled  TRUE
  SFNode [in,out] metadata NULL [X3DMetadataObject]
  SFBool [out]    isActive
}
</pre>

<p>This abstract node type is the base type for all sensors.</p>


<h1><img class="cube" src="../../Images/cube.gif" alt="cube">
<a name="Nodereference"></a>
7.4 Node reference</h1>

<h2><a name="MetadataDouble"></a>7.4.1 MetadataDouble</h2>
<pre class="node">MetadataDouble : X3DNode, X3DMetadataObject {
  SFNode   [in,out] metadata  NULL [X3DMetadataObject]
  SFString [in,out] name      &quot;&quot;
  SFString [in,out] reference &quot;&quot;
  MFDouble [in,out] value     []
}</pre>
<p>The metadata provided by this node is contained in the double-precision 
floating point numbers of the <i>value</i> field.</p>
<h2><a name="MetadataFloat"></a>7.4.2 MetadataFloat</h2>
<pre class="node">MetadataFloat : X3DNode, X3DMetadataObject { 
  SFNode   [in,out] metadata  NULL [X3DMetadataObject]
  SFString [in,out] name      &quot;&quot;
  SFString [in,out] reference &quot;&quot;
  MFFloat  [in,out] value     []
}</pre>
<p>The metadata provided by this node is contained in the single-precision 
floating point numbers of the <i>value</i> field.</p>
<h2><a name="MetadataInteger"></a>7.4.3 MetadataInteger</h2>
<pre class="node">MetadataInteger : X3DNode, X3DMetadataObject { 
  SFNode   [in,out] metadata  NULL [X3DMetadataObject]
  SFString [in,out] name      &quot;&quot;
  SFString [in,out] reference &quot;&quot;
  MFInt32  [in,out] value     []
}</pre>
<p>The metadata provided by this node is contained in the integers of the <i>
value</i> field.</p>
<h2><a name="MetadataSet"></a>7.4.4 MetadataSet</h2>
<pre class="node">MetadataSet : X3DNode, X3DMetadataObject { 
  SFNode   [in,out] metadata  NULL [X3DMetadataObject]
  SFString [in,out] name      &quot;&quot;
  SFString [in,out] reference &quot;&quot;
  MFNode   [in,out] value     [] [X3DMetadataObject]
}</pre>
<p>The metadata provided by this node is contained in the metadata nodes of the
<i>value</i> field.</p>
<h2><a name="MetadataString"></a>7.4.5 MetadataString</h2>
<pre class="node">MetadataString : X3DNode, X3DMetadataObject { 
  SFNode   [in,out] metadata  NULL [X3DMetadataObject]
  SFString [in,out] name      &quot;&quot;
  SFString [in,out] reference &quot;&quot;
  MFString [in,out] value     []
}</pre>
<p>The metadata provided by this node is contained in the strings of the <i>
value</i> field.</p>

<h2><a name="WorldInfo"></a>7.4.6 WorldInfo</h2>

<pre class="node">WorldInfo : X3DInfoNode { 
  SFNode   [in,out] metadata NULL [X3DMetadataObject]
  MFString []       info     []
  SFString []       title    ""
}
</pre>

<p>The WorldInfo node contains information about the world. This node is strictly 
  for documentation purposes and has no effect on the visual appearance or behaviour 
  of the world. The <i>title</i> field is intended to store the name or title 
  of the world so that browsers can present this to the user (perhaps in the window 
  border). Any other information about the world can be stored in the <i>info</i> 
  field, such as author information, copyright, and usage instructions.</p>



<h1><img class="cube" src="../../Images/cube.gif" alt="cube">
<a name="SupportLevels"></a>7.5 Support levels</h1>

<p>The Core component provides two levels of support as specified in
<a href="#t-Coresupportlevels">Table 7.2</a>. Level 1 provides the minimum basis for 
all profiles and components. Level 2 adds support for prototypes.</p>

<div class="CenterDiv">

<p class="TableCaption">
<a name="t-Coresupportlevels"></a>
Table 7.2 &#8212; Core component support levels</p>

    <table>
      <tr> 
        <th><b>Level</b></th>
        <th>Prerequisites</th>
        <th><b>Nodes/Features</b></th>
        <th>Support</th>
      </tr>
      <tr> 
        <td align="center"><b>1</b></td>
        <td>None</td>
        <td></td>
        <td></td>
      </tr>
      <tr> 
        <td align="center"></td>
        <td></td>
        <td><i>X3DBindableNode</i> (abstract)</td>
        <td>n/a</td>
      </tr>
      <tr> 
        <td align="center">&nbsp;</td>
        <td>&nbsp;</td>
        <td><i>X3DChildNode</i> (abstract)</td>
        <td>n/a</td>
      </tr>
      <tr> 
        <td align="center"></td>
        <td></td>
        <td><i>X3DField</i> (abstract)</td>
        <td>n/a</td>
      </tr>
      <tr> 
        <td align="center">&nbsp;</td>
        <td>&nbsp;</td>
        <td><i>X3DInfoNode</i> (abstract)</td>
        <td>n/a</td>
      </tr>
      <tr> 
        <td align="center">&nbsp;</td>
        <td>&nbsp;</td>
        <td><i>X3DMetadataObject</i> (abstract)</td>
        <td>n/a</td>
      </tr>
      <tr> 
        <td align="center"></td>
        <td></td>
        <td><i>X3DNode</i> (abstract)</td>
        <td>n/a</td>
      </tr>
      <tr> 
        <td align="center"></td>
        <td></td>
        <td><i>X3DObject</i> (abstract)</td>
        <td>n/a</td>
      </tr>
      <tr> 
        <td align="center"></td>
        <td></td>
        <td><i>X3DPrototypeInstance</i> (abstract)</td>
        <td>n/a</td>
      </tr>
      <tr> 
        <td align="center"></td>
        <td></td>
        <td><i>X3DUrlObject</i> (abstract)</td>
        <td>n/a</td>
      </tr>
      <tr> 
        <td align="center">&nbsp;</td>
        <td>&nbsp;</td>
        <td>MetadataDouble</td>
        <td>All fields are fully supported.</td>
      </tr>
      <tr> 
        <td align="center">&nbsp;</td>
        <td>&nbsp;</td>
        <td>MetadataFloat</td>
        <td>All fields are fully supported.</td>
      </tr>
      <tr> 
        <td align="center">&nbsp;</td>
        <td>&nbsp;</td>
        <td>MetadataInteger</td>
        <td>All fields are fully supported.</td>
      </tr>
      <tr> 
        <td align="center">&nbsp;</td>
        <td>&nbsp;</td>
        <td>MetadataSet</td>
        <td>All fields are fully supported.</td>
      </tr>
      <tr> 
        <td align="center">&nbsp;</td>
        <td>&nbsp;</td>
        <td>MetadataString</td>
        <td>All fields are fully supported.</td>
      </tr>
      <tr> 
        <td align="center">&nbsp;</td>
        <td>&nbsp;</td>
        <td>WorldInfo</td>
        <td>All fields are fully supported.</td>
      </tr>
      <tr>
        <td align="center">&nbsp;</td>
        <td>&nbsp;</td>
        <td> Statements:<br>
&nbsp; Header<br>
&nbsp; PROFILE<br>
&nbsp; COMPONENT<br>
&nbsp; META</td>
        <td>Full support.</td>
      </tr>
      <tr> 
        <td align="center"></td>
        <td></td>
        <td>Field types</td>
        <td>All field types.<br>
        </td>
      </tr>
      <tr> 
        <td align="center"></td>
        <td></td>
        <td>Event model</td>
        <td>As specified in 
<a href="../concepts.html#EventModel">4.4.8 Event Model</a>.</td>
      </tr>
      <tr> 
        <td align="center"></td>
        <td></td>
        <td>Routing</td>
        <td> 
          <p>Full support.</p>
          </td>
      </tr>
      <tr> 
        <td align="center"></td>
        <td></td>
        <td>Prototyping</td>
        <td>Optionally supported.</td>
      </tr>
      <tr> 
        <td align="center"><b>2</b></td>
        <td>None</td>
        <td> </td>
        <td>&nbsp;</td>
      </tr>
      <tr> 
        <td align="center"></td>
        <td></td>
        <td>All Level 1 Core objects</td>
        <td>As supported in Level 1.</td>
      </tr>
      <tr> 
        <td align="center"></td>
        <td></td>
        <td>Prototyping</td>
        <td>Full support.</td>
      </tr>
    </table>
</div>

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